The present invention relates to a technology which suppresses damage to an electronic circuit by radiation in a radiation detector module.
As a detector module that configures a radiation detector, there has been proposed one in which an electronic circuit that processes output signals of detecting elements is arranged on the back surface of a detecting element array (refer to, for example, FIG. 2 of Japanese Patent Laid-Open No. 2013-170922 and FIGS. 2 and the like of Japanese Patent Laid-Open No. 2012-210291). Such a configuration aims at shortening a connecting line between each detecting element and the electronic circuit as much as possible to thereby prevent the mixing of external noise to the output signal of the detecting element and eliminating routing of each connecting line to make a structure simple.
On the other hand, the detecting element array often includes a plurality of detecting elements arranged in a matrix form, and a wall structure formed to a lattice shape so as to divide the detecting elements respectively. Generally, if each detecting element is of a combination of a scintillator that converts incident X-rays to light and a photoelectric conversion element that converts the light to an electric signal, the wall structure becomes a reflector for reflecting light emitted from the scintillator and efficiently guiding the light on the photoelectric conversion element. The wall structure that functions as the reflector normally has X-ray permeability. The electronic circuit, particularly one including an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or the like is substantially degraded in performance when irradiated with X-rays. That is, of radiation applied from a radiation tube to a detector, the radiation incident on each grid portion of the wall structure penetrates the wall structure as it is, and reaches the electronic circuit provided on the back side, thereby causing damage to the electronic circuit.
The following countermeasure has heretofore been proposed to prevent such damage. For example, there is cited a method of sticking a lattice-like radiation shielding grid including a heavy metal such as tungsten onto each grid portion of a wall structure in alignment therewith and preventing radiation from penetrating the grid portions of the wall structure.
The method using such a lattice-like radiation shielding grid is however accompanied by several problems.
For example, since the width of the radiation shielding grid often becomes very thin (e.g., about 0.2 mm), it is often fabricated by high-cost etching processing.
Further, for example, collimator plates for scattered ray removal are normally respectively disposed at positions corresponding to grid portions of a wall structure extending in a slice direction. That is, radiation does not almost arrive at the grid portions of the wall structure extending in the slice direction by a radiation shielding effect by the collimator plates. Therefore, although the grid portions extending in the slice direction at the radiation shielding grid are originally unnecessary, they are provided with another objective of mechanically supporting grid portions extending in a channel direction at the radiation shielding grid. Now consider where the width of each of the grid portions extending in the slice direction at the radiation shielding grid is temporarily not to be sufficiently smaller than the thickness of each collimator plate. In this case, mutual position errors between the collimator plates and the grid portions cause a variation in the radiation shielding effect. This will change a radiation spectrum, the intensity of scattered radiation and the like, thus causing an artifact in a reconstructed image. There is therefore a need to finish each grid portion extending in the slice direction at the radiation shielding grid more finely (e.g., less than ⅔ of the thickness of each collimator plate) by etching processing. Such processing is however very difficult technically and incurs high cost.
With the foregoing in view, there has been a demand for a detector module equipped with a detecting element array that has a plurality of detecting elements arranged in a matrix form in first and second directions orthogonal to each other and that allows radiation to penetrate through spaces defined between the detecting elements, and an electronic circuit arranged on the radiation emission side of the detecting element array. This configuration eliminates radiation shielding materials extending in the second direction while shielding against radiation in the spaces defined between the detecting elements in the second direction.